A 29-year-old primigravida at 33 weeks with severe pre-eclampsia is receiving IV magnesium sulfate at 2 g/hour. Her deep tendon reflexes are present, respiratory rate is 14/min, and urine output is 30 mL/hour. Her serum magnesium level is 7.2 mEq/L. Which of the following best describes the clinical significance of this level?

• A Subtherapeutic level; increase infusion rate to 3 g/hour
• B Borderly elevated; reduce infusion rate to 1 g/hour
• C Toxic level; stop infusion and give calcium gluconate
• D Therapeutic level; continue current infusion rate ✓

Explanation

The therapeutic range for magnesium sulfate in pre-eclampsia is 4-7 mEq/L (some texts cite up to 7.5 mEq/L). A level of 7.2 mEq/L is within the therapeutic range. Toxicity typically manifests at levels above 8-10 mEq/L, with loss of deep tendon reflexes at 10-12 mEq/L and respiratory arrest at 15-20 mEq/L. Since reflexes are present and respiratory rate is normal, the current rate should be continued with ongoing monitoring.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.